Cancer is a multigenic disease affecting 1/3 people at some point in their lifetime. Cancer is a multi-step process that relies on the successive mutations of key signaling, cell cycle or cell adhesion pathways to generate metastatic tumors. Since cancer arises from mostly normal cells and develops surrounded by normal cells, which are known to be involved in tumorigenic process, it is highly important to study the process of tumorigenesis in vivo. We propose here, to examine the process of tumorigenesis by using an unbiased approach in a whole non-mammalian animal model system, that of the vinegar fly, Drosophila. Due to the evolutionary conservation of signaling, cell cycle and cell adhesion pathways, studies carried out in Drosophila are highly relevant to mammals. We will examine 2 tumor suppressor genes, scribble and D-cbl and the oncogene, activated ras (ras-ACT), in the process of tumorigenesis. These genes function via different pathways in cellular regulation. Scribble is a scaffolding protein involved in apical-basal polarity, but may also have a role in modulating intracellular signaling. Cbl is an E3 ubiquitin ligase involved in down-regulation of transmembrane receptor signaling. ras is a signaling GTPase that acts downstream of growth factor receptors. We have shown that ras-ACT cooperates with scribble and D-cbl mutants to enhance their tumorigenic phenotypes. The overall aim of this proposal is to use the semi-neoplastic phenotypes generated by clones of scribble, D-cbl or ras-ACT mutants within a wild-type background to investigate the process of tumorigenesis in vivo. Specifically, the aims of this project are to: (1) Identify genes that when over-expressed cooperate with the scribble, D-cbl or ras-ACT mutants in inducing neoplasia, by using phenotypes generated by clones of these mutants in the Drosophila eye. These screens will allow us to systematically identify novel cooperating oncogenes in a whole animal system. (2) Identify genes when over-expressed specifically in wild-type tissue (but not in the scribble mutant tissue) rescue or enhance the phenotype caused by scribble-induced neoplasia in the eye. This screen will allow us to systematically identify genes that are expressed in wild-type cells that can act as tumor-promoting or anti-tumor genes. These screens will enable us to identify novel cooperating cancer-causing genes and anti-tumor genes within a whole animal system. The ultimate goal is to use this knowledge as a means to develop new targets for anti-cancer therapy.